Hi Lorenzo
You can give your buttons the same name but set different values for them, then use the
$this->data("button_name")
in your code, or use the Event Switcher action directly:

Max, ChronoForms developer
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Hi Lorenzo
The solution I proposed sets the value in the HTML element itself, the button "value" attribute, do you need to unset this ?
Your event switcher will be in the "Submit" event of that page as you need, if you go back then the button values stay the same
Max, ChronoForms developer
ChronoMyAdmin: Database administration within Joomla, no phpMyAdmin needed.
ChronoMails simplifies Joomla email: newsletters, logging, and custom templates.
Hi Lorenzo
Could you please post a screenshot of your submit area so that I can understand this better ?
Max, ChronoForms developer
ChronoMyAdmin: Database administration within Joomla, no phpMyAdmin needed.
ChronoMails simplifies Joomla email: newsletters, logging, and custom templates.
Hi Lorenzo
So you can delete or disable the PHP action, change the 3 buttons names to "next", and set the value for each one as I show earlier, the values should be "annulla", "next_no" and "next_yes", then in your Event Switcher use {data:next} in the Switch Value:

Did you try that ?
Max, ChronoForms developer
ChronoMyAdmin: Database administration within Joomla, no phpMyAdmin needed.
ChronoMails simplifies Joomla email: newsletters, logging, and custom templates.